Shock resistant transducer



RELATIVE 0 u TPUT (sec- Oct. 17, 1967 E. v. cARLsoN 3,347,991

SHOCK RESISTANT TRANSDUCER Filed March 17, 1964 2 Sheets-$heet 1 INVENTOR.

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E. V. CARLSOM SHOCK RESISTANT TRANSDUCER Get. 17, we?

2 sheets-sheet 2 Filed March 17, 1964 United States Patent O 3,347,991 SHOCK RESISTANT TRANSDUCER Elmer V. Carlson, Prospect Heights, 111., assignor to Industrial Research Products, Inc., Elk Grove Village, III., a corporation of Delaware Filed Mar. 17, 1964, Ser. No. 352,462 Claims. (Cl. 179-114) ABSTRACT OF THE DISCLGSURE A transducer and a method of making the transducer. The transducer having a vibratable armature and resilient material secured to the armature for holding the armature relative to the remainder of the transducer. The method including the steps of magnetically balancing the transducer by magnetically positioning the armature, flowing a material between the armature and a fixed portion of the transducer, and then solidifying the material.

This invention relates to a method of shock protecting a vibratable armature of a transducer, and to the means for practicing this method. The invention is particularly applicable to that type of armature which exhibits a node of vibration other than where it is securely coupled to the frame. A node occurs at that portion which is a portion that remains at rest during vibration.

The invention is disclosed in connection with those types of armatures which have one end rigidly held at a point near the vibratable end. The two ends are connected by a section which is spaced away from the two ends. Thus, in applicants United States Letters Patent No. 3,111,563, dated Nov. 19, 1963, an E-armature has a desirable node extending across the base which connects the three arms to each other. The geometry of this armature is such that when the frequency approaches 6,000 c.p.s., a node develops adjacent the line of joinder of the armature to the drive pin and decreases the desired vibration of the armature-drive pin-diaphragm assembly. There is a decline in response as indicated by the shaded area in FIGURE 6 of this application. However, as said patent discloses, by holding the armature at a desirable node, the undesirable nodes do not develop. Rigidly holding the vibratable portion at a node appears to render the armature less susceptible to shock damage than when it is wholly unrestrained.

An object of this invention is to provide an elastic means between the armature and the transducer which will not interfere with useful vibration-but will provide shock protection.

Returning to the structure shown in said patent, the anchoring of the armature is described in column 4, lines 23, et seq. It is done before final adjustment of the armature. This step is performed after the transducer has been sealed in its case and the previous anchoring of the armature at a node interferes with this adjustment.

Accordingly, it is another object of this invention to provide a method of anchoring armatures at nodes after final adjustment has been made. A feature of this invention is introducing the anchor through an opening in the case after final adjustment.

Another object of this invention is to utilize an elastic material between the armature and the anchoring means to absorb energy developed when a dropped transducer strikes an obstacle. A feature of this invention is the use of an elastomer as the anchor. The elastomer is flowable at room temperatures so that it may be squeezed into position and thereafter is cured in situ. This elastomer after curing has displacement characteristics which are nonlineal as compared to a spring.

3,347,091 Patented Oct. 17, 1967 Another object of this invention is to utilize a part standard to the transducer but capable of holding the armature as finally adjusted to magnetically balance the transducer. When one tries to hold the armature by a means mounted through the opening of the case, or inserted through the opening and then mounted on the inside of the case, or premounted therein, without altering the adjusted armature, one has to compensate, because an armature in one transducer does not bear the same relationship to the opening in the case as an adjusted armature in the transducer next on the assembly line. The use of a standard holding means which rigidly grasps the armature would of itself destroy the adjustment of the armature. One feature of this invention is the use of two parallel rigid plane surfaces mounted on a single head which can be placed in a fixed position in the opening of any transducer. The two flat surfaces are spaced from each other by a distance greater than the maximum distortion of the armature due to adjusting. This space is filled with a freely flowable elastomer before the anchor is inserted in the opening. When it is inserted, the two flat surfaces straddle the armature which displaces the elastomer by its own volume and at its own position in between the two surfaces. Thus, if after adjustment, an armature is exactly centered in the space 0ccupied by the elastomer between the two surfaces, there will be an equal amount of elastomer after curing on the two sides of the armature, and the armature will be equally well protected from shock in either direction. If, however, after adjustment the armature is not so centered, then the freely flowing elastomer compensates, so that there will be, after curing, more elastomer on one side than on the other. This diminishes shock protection slightly, but the advantage of being able to get anchoring of the armature by standard parts without altering the adjustment outweighs this slight deficiency. It will be appreciated that depending upon the thickness of the elastomer band, the amount of shock protection afforded can be increased or decreased.

These and such other objects as may hereinafter appear are disclosed in several embodiments of the invention which are described in connection with the drawings, wherein:

FIGURE 1 is a cut-away view in perspective of a transducer having an E-armature as in FIGURE 1 of US. Patent No. 3,111,563, with an anchor of this invention applied;

FIGURE 2 is a cut-away view in perspective of a transducer having an E-armature with flange as in FIGURE 1 of copending application Ser. No. 298,332 with anchor applied;

FIGURE 3 is a view taken 0 nthe line 3-3 of FIG- URE 1;

FIGURE 4 is a side elevation of the anchor;

FIGURE 5 is an end elevation of the stem end of the anchor;

FIGURE 6 is a graph illustrating loss of response above the principal resonance in an unanchored armature;

FIGURE 7 is a view of another embodiment as if taken on the line 77 of FIGURE 1 and showing the positioning of an elastic material between the tunnel wall of the coil and the two surfaces of the central vibratable arm of the armature near a major node;

FIGURE 8 is a view of the embodiment of FIGURE 7 as if taken on the line 88 of FIGURE 1;

FIGURE 9 is a schematic, perspective view of an E- shaped armature showing the nodes;

FIGURE 10 is a schematic, perspective view of a U- shaped armature showing the nodes;

FIGURE 11 is a schematic, perspective view of an armature which is E-shaped in side elevation; and

FIGURE 12 is a schematic, perspective view of an armature which is U-shaped in side elevation.

Continuing to refer to the drawings, FIGURE 1 discloses a cut-away transducer of the type shown in United States Letters Patent No. 3,111,563. The flux-conductive cup 22 forming the main body of the case houses a magnet stack 26 which clamps the ends of two outside arms 28 and 38 of an E-shaped armature having a central vibratable arm 32 and a back or base member 33, the ends of the arms 23 and 39 being clamped in the magnet stack 26. The vibrataable arm 32 is connected by a drive pin 36 to a diaphragm 38 and the whole is enclosed by a fluxconductive cover 40. A flux-conducted bulkhead 24 con tacts the upper side of the magnet stack 26 and is in flux conductive relationship with the cover 49 and the cut 22, both of which are flux conductive so that the direct fiux circut flows through the case while the signal circuit is confined within the case. The coil 41 contains the tunnel through which passes the arm 32 of the armature.

The entire armature is free to vibrate excepting for the two ends in the clamped gaps 68 and 7d. The armature has a node which extends along the dot-dash line 18, 16 and 14, although a better representatiton of this node may be along the curved dash line 19, see FIGURE 9. In this area during vibration, the armature is substantially still. At higher frequencies, as illustrated in FIGURE 1, this armature develops a node near the dotted line 21, which is adjacent to the point of joinder of the drive pin 36 with the middle arm 32 of the armature. The useful vibration of the armature at the frequencies shown in FIGURE 6 in the shaded area is diminished by a node which develops along the line 21 adjacent the drive pin 36. If the armature is being held at one or more of the areas 18, 16 and 14 or along the line 19, this undesirable node at 21 does not develop. The principal difficulty with the means shown for holding the armature at the node in applicants said patent is that it is applied before adjustment of the armature.

Mounted in the opening 42 of the case is an anchor 10 which through an elastic elastomer grasps opposite sides of the armature at a node. Optionally, a second anchor 12 may be mounted in transverse alignment with the first.

Applicant pursues the following method of anchoring an armature at a node. The transducer is assembled as shown in FIGURE 1 with the cover 40 sealed to the bottom cup 22, and with at least one opening 42 in a side wall. A tool is inserted through this opening 42 and the armature is grasped at approximately the same place that the anchor 10 is grasping the armature, that is, it has a slotted end which may be twisted so as to raise or lower the middle arm 32 of the armature in the working gap 34. This is done with leads of the coil connected to a testing circuit, all of which is old in the art. When the test apparatus indicates that there will be substantially no flow of flux in either direction when the armature is at rest, the tool is withdrawn.

Thereupon, applicant takes an anchor shown in perspective in FIGURES l and 2 and in detail in FIGURES 3, 4 and 5. This anchor 44. has a head 46 and a shank 48 with a central slot t) down the shank to provide two tines 52 and 54 having facing inside surfaces. These surfaces are spaced by a distance sufficient to enable the shank 48 to be inserted through the opening 42 and rigidly held there while still providing clearance between the armature and either inside surface of the tines 52 and 54. Thus applicant is able to use a standard fitting on the anchor 44 for a standard hole 42 in the case 22 to place the anchor in operative holding position with respect to the armature.

Applicant then fills the slot 50 with a fiowable elastorner 58. He next inserts the shank 52 through the opening 42 with the inside walls of the slots parallel to the outside surfaces of the armature arm 36. The armature arm displaces sufiicient elastomer so that the cross section of the parts shown in FIGURE 3 is attained. If the arm 30 occupies the dotted-line position 31, shown in FIGURE 3 wherein the armature is closer to the tine 52 than to the tine 54, the armature will not change its adjusted position but will simply end closer to the tine 52 than to the line 54 with elastorner therebetween. With the anchor 44 rigidly fixed by adhesive or welding to the case 22, the elastomer is then caused to harden either by mere exposure to air due to its nature or by chemical or heat curing.

Applicant uses an elastomer. Any elastorner that can be flowed and then solidified will do so long as its volume does not appreciably change upon solidifying. Elastomers can be cured at temperatures which will not harm the other parts of the transducer, and they remain resilient in the solid state. Although not appreciably compressible, an elastomer squeezes out of and back into the space occupied by it, see FIGURES 3 and 8, and its resistance to deformation is not linear but increases incrementally with deformation. Many other materials can be used. Thus, if one wants the armature rigidly held at a node as in Patent No. 3,111,563, that is, if one does not seek shock protection, almost any flowable plastic that will set after it has passed through a given temperature, may be used. A suitably plasticized epoxy resin or a plasticized cellulose nitrate may be used. Colloidal rubbers are available and these will give an end result similar to elastomers.

The method may be practiced by introducing the elastomer through the opening in the case directly between a portion of the armature and a fixed portion of the transducer or case. Using a fine tube 43, positioned through an opening in the case, the elastomer is forced between one surface of the armature and the adjacent edge of the coil tunnel, that is, the tunnel end away from the working gap. When an elastomer having adhesive properties is used, the elastomer need be on but one side of the armature. However, applicant in practice places the elastomer on both sides. In FIGURES 7 and 8, the elastomer 64 is immediately adjacent a node and the coil tunnel is in fixed position because the coil is cemented to the inside of the case. Alternately, brackets 29 attached to the case wall can be used to retain the elastomer 27 which is inserted after adjustment through the opening which is shown closed by cover 31.

Ideally, the elastomer is positioned between a flat surface on a node of the armature and an adjacent, somewhat parallel fiat surface mounted on a fixed structure. It happens that the upper and lower walls of the coil tunnel are parallel to the adjacent opposite surfaces of the armature. These opposed surfaces were intentionally provided with the tines 52 and 54. However, the surfaces need not be parallel because the flowable elastomer will compensate for irregularities. In FIGURE 5, applicant shows in dotted lines 53 and 55, tapered walls on the inside surfaces of the anchor.

In FIGURES 9 through 12, applicant presents schematically several types of armatures that are suitable for holding at a note. FIGURE 9 is a schematic view of the E-armature heretofore described. In FIGURE 10, applicant shows a U-armature which is held at a fixed gap with a working gap adjacent 82. This armature develops a node along the line 84. It will be adjusted by twisting at about 86. The armature should be held at some place along the dash line 84. Applicant could put an opening in the case adjacent the point 88 and adjust here, in which event it would be convenient to mount his anchor at this point.

In FIGURES 11 and 12, applicant shows schematic views of armatures which in cross section are U- and E-shaped. In FIGURE 12, 90 and 92 are magnets or pole pieces which are held in fixed relationship in a transducer. An armature 94 is mounted rigidly to the transducer frame 95 in flux-conductive relationship to such pole pieces or magnets. This U-shaped armature will develop a node along the aXis 96. Within the working frequency range of the transducer, there may develop an undesirable node near the tip of the arrow 98, that is, near the drive pin 101 which is connected to a diaphragm. This undesirable node can be very substantially suppressed and the ruggedness of the armature increased by positioning an anchor 101 in the pivotal line 96.

In FIGURE 11, applicant shows an armature having an E-shaped armature in cross section. The center arm 102 is free to vibrate while the upper and lower arms are held fixed at 112 and 114. This armature 104 has a node along the pivotal line 1105. Again, this armature will develop an undesirable node adjacent the drive pin 196 at 108. By positioning an anchor 110 at 1154, Which anchor is rigidly fastened to other parts of the trans ducer or to the case, the undesirable node 108 will be restrained and the possibility of deforming the armature by inertial forces will be decreased.

The transducer in FIGURE 2 is presented because the base member 29 of the E-armature is at right angles to the plane of the armature. The desirable nodes occur at the areas engaged by the anchor 46 on arm 30 and one not shown on arm 28. The armature need be held at only one area in the node.

Having thus described my invention, what I claim is:

1. A transducer comprising a motor, an armature having a pair of substantially fiat opposite surfaces, said armature having one end fixedly mounted on said motor and having another end vibratable along an axis normal to a portion of said flat opposite surfaces, and resilient means fixedly mounted in relation to the transducer and engaging both of said fiat opposite surfaces of the armature in its vibratable portion between said fixed end and said vibratable end for holding movement of the armature in a plane substantially perpendicular to said axis within fixed limits.

2. The transducer of claim 1 wherein the armature is of a type that develops a node and the resilient means engages the armature only at that node.

3. The transducer of claim 1 wherein the tunnel of a coil surrounds the armature between the fixed end and the vibratable end and the resilient material occupies a portion of the space between the tunnel wall and the opposed flat surfaces of the armature.

4. The transducer of claim 1 wherein the transducer is in a case, a portion of the armature is adjacent to one wall of the case, a port is disposed in said wall, spaced members are rigidly mounted on the case, said members extending inwardly and straddling the armatture, and wherein the resilient material is positioned between said members and adjacent surfaces of the armature.

5. The transducer of claim 1 wherein One end of the armature is held rigidly in the transducer at a point near the vibratable end with a section remote from the ends joining them together, and wherein the resilient means engages the armature at a node.

6. The transducer of claim 1 wherein the armature has an E-shape with the vibratable end being the end of the middle arm, and wherein the resilient means engages opposite sides of the armature near the junction of one outside arm and the cross arm.

'7. The transducer of claim 1 wherein a case houses the assembly and has a port through its wall adjacent a vibratable portion of the armature spaced from the vibratable end, and wherein a plug having a shank with an openended slot therein is mounted in the port with a portion of the armature in the slot, and wherein the resilient material spaces the walls of the slot from opposite surfaces of the armature.

8. An electroacoustic transducer comprising a case, a motor mounted therein, a fiat E-armature having each end of its outer legs fixedly mounted on said motor and having the end of its center leg mounted in a flux working gap of said motor, a coil around the center leg with the walls of its tunnel spaced therefrom, and a resilient material positioned between the walls of the tunnel and the opposite surfaces of the armature.

9. The transducer of claim 8 wherein the resilient material extends lengthwise of the central leg for approximately the same distance as the tunnel wall is spaced from the armature.

10. An electroacoustic transducer comprising a case, a motor mounted therein, a flat E-armature having each end of its outer legs fixedly mounted on said motor and having the end of its center leg mounted in a flux working gap of said motor, a port in the wall of the case adjacent the edge of the armature at the junction of an outside arm and the cross arm, a plug over said port, a stem on the inside of the plug, an axial slot in said stem straddling the armature, and resilient material between each wall of the slot and the adjacent wall of the anmature.

References Cited UNITED STATES PATENTS 3,163,723 12/1964 Tibbetts 1791 14 FOREIGN PATENTS 1,044,169 11/ 1958 Germany.

KATHLEEN H. CLAFFY, Primary Examiner.

A. MCGILL, Assistant Examiner. 

1. A TRANSDUCER COMPRISING A MOTOR, AN ARMATURE HAVING A PAIR OF SUBSTANTIALLY FLAT OPPOSITE SURFACES, SAID ARMATURE HAVING ONE END FIXEDLY MOUNTED ON SAID MOTOR AND HAVING ANOTHER END VIBRATABLE ALONG AN AXIS NORMAL TO A PORTION OF SAID FLAT OPPOSTIE SURFACES, AND RESILIENT MEANS FIXEDLY MOUNTED IN RELATION TO THE TRANSDUCER AND ENGAGING BOTH OF SAID FLAT OPPOSITE SURFACES OF THE ARMA- 